Vibration of chimneys exposed to wind and pilings exposed to ocean currents has been mentioned in numerous United States patents. For example, U.S. Pat. Nos. 3,352,118; 3,383,869 and 4,230,423 all discuss marine pilings but do not suggest that helical ribs could be useful for shedding vortices or minimizing vortex formation. Surface protuberances are suggested in several United States patents, such as U.S. Pat. Nos. 4,193,234; 4,059,129; 3,581,449, 2,604,838 and 3,076,533.
Feis U.S. Pat. No. 4,059,129 shows protrusions formed as segments of helical ribs arrayed in vertical rows on chimneys.
Scruton U.S. Pat. No. 3,076,533 shows helical ribs protruding from the outer surface of chimneys exposed to wind and recommends particular parameters and ratios for the shape of such ribs. For example, Scruton U.S. Pat. No. 3,076,533 shows in its FIG. 3 a wind tunnel model of a chimney with three protruding ribs extending outward from its peripheral surface, at a pitch of approximately 12 times the diameter of the chimney. The text in columns 1 and 4 of this patent mentions that the optimum helix pitch for three equiangularly spaced strakes is of the order of 15 times the diameter or characteristic transverse dimension D. In column 4, ribs or strakes of different heights extending radially from the outer surface of the chimney are described, with heights ranging from 0.029 D to 0.118 D, stating that at 0.118 D the aeolian instability is "reduced to a very small area and only a very small value of structural damping is required to eliminate the oscillations."
This Scruton patent indicates that round stacks should never require strakes higher than 1/8 of D, even when minimum damping is provided by the solid structure itself.
Helical ribs employed for vortex shedding are suggested for overhead wires or cables exposed to the wind, in Zaltsberg U.S. Pat. No. 4,549,035 and Little U.S. Pat. No. 3,105,866; or for towing lines or towed cables exposed to the ocean in Fabula U.S. Pat. No. 3,884,173 and Cohen U.S. Pat. No. 3,991,550. In each of these four patents a single helical rib or strake is employed, and the relative movement of the body of fluid in which the solid object is immersed is not always transverse to the axis of the object; in all these cases it may be in many different directions, some nearly parallel to the axis of the object itself.